Background: Exercise stimulates the vascular response in pathological conditions, including ischemia; however, the molecular mechanisms by which exercise improves the impaired hypoxia-induced factor (HIF)-1α-mediated response to hypoxia associated with aging are poorly understood. Here, we report that swimming training (ST) modulates the vascular response to ischemia in aged (24-month-old) mice. Methods and Results: Aged wild-type mice (MMP-2 +/+) that maintained ST (swimming 1 h/d) from day 1 after surgery were randomly assigned to 4 groups that were treated with either vehicle, LY294002, or deferoxamine for 14 days. Mice that were maintained in a sedentary condition served as controls. ST increased blood flow, capillary density, and levels of p-Akt, HIF-1α, vascular endothelial growth factor, Fit-1, and matrix metalloproteinase-2 (MMP-2+/+) in MMP-2 mice. ST also increased the numbers of circulating endothelial progenitor cells and their function associated with activation of HIF-1α. All of these effects were diminished by LY294002, an inhibitor of phosphatidylinositol 3-kinase; enhanced by deferoxamine, an HIF-1α stabilizer; and impaired by knockout of MMP-2. Finally, bone marrow transplantation confirmed that ST enhanced endothelial progenitor cell homing to ischemic sites in aged mice. Conclusions-: ST can improve neovascularization in response to hypoxia via a phosphatidylinositol 3-kinase-dependent mechanism that is mediated by the HIF-1α/vascular endothelial growth factor/MMP-2 pathway in advanced age. © 2010 American Heart Association, Inc.